4ohm Amp into an 8ohm cab

[lidl e]

While I've been playing for years i do have a bit of a rookie question. I do always try to match impedance, currently my only available amp head is a TC electronic bh250. The documentation says run a 4ohm load onto it.

I have only ever used it with a single 8ohm cab.

Am i risking anything by doing that? I never considered it was an issue. I didnt even realise the TC was considered 4ohm. I just happened to check the manual in prep of a few shows that are coming up.

I played some shows recently with a bigger band using the bh250 into a SWR Goliath III and it sounded great. I even let the headliner (the aquabats) use my setup and it sounded great.

We are about to do a mini tour and i was planning on using this setup but i wont have a backup if something goes wrong.

Am i right to be worried? I could conceivably bring an extra Aguilar 1x12 which is 8 ohms to give me 4ohm total but storage space is at a premium.

I dont really want to invest in another head. I do have an old SWR Mo Bass but i need to bring an external transformer to use that as it is from the US and I am im the EU.

I have used the tc into a single 8ohm speaker many times. The tc and the aggie cab seem to work well.

Cheers, all.

 

[DJ Bebop]

No problem running an 8-ohm cabinet off of an amp with a 4-ohm minimum load rating.

The amp is telling you not to run anything less than 4 ohms where it makes its full power of 250 watts. At 8 ohms you are getting half of its full rated power, probably about 125 watts. No harm should come to it if you don't use a load less than 4 ohms.

An extra 8-ohm cabinet would give the full power output and more stage volume and presence but if you have been happy with your rig up to this point have used it on big stages before and you don't have the room to bring more, it will have to work.

A second cab could be idea though, don't need it but it's there if you do

 

[smogg]

^^^^ this ^^^^

 

[lidl e]

No problem running an 8-ohm cabinet off of an amp with a 4-ohm minimum load rating.

The amp is telling you not to run anything less than 4 ohms where it makes its full power of 250 watts. At 8 ohms you are getting half of its full rated power, probably about 125 watts. No harm should come to it if you don't use a load less than 4 ohms.

An extra 8-ohm cabinet would give the full power output and more stage volume and presence but if you have been happy with your rig up to this point have used it on big stages before and you don't have the room to bring more, it will have to work.

A second cab could be idea though, don't need it but it's there if you do

Cheers, bud.

Would adding the extra 1x12 be a good idea so id get the full power? I believe it is rated for 400 watts so shoildnt be an issue handling it. The SWR can take 500+

Is a 4x10 and a 1x12 an odd combo?

 

[smogg]

Cheers, bud.

Would adding the extra 1x12 be a good idea so id get the full power? I believe it is rated for 400 watts so shoildnt be an issue handling it. The SWR can take 500+

Is a 4x10 and a 1x12 an odd combo?

IMHO 112 + 410 is not an ideal combination. The 112 will probably run out of headroom long before the 410 resulting in little if any volume gain.

 

[lidl e]

IMHO 112 + 410 is not an ideal combination. The 112 will probably run out of headroom long before the 410 resulting in little if any volume gain.

Yeah. Agreed but it would give me the full 250 watts, no? I assume that would make a difference? The aguilar is rated at 300 watts ( the older GS112)

 

[agedhorse]

Worrying g about getting the most power out of the amp isn’t important. If what you are doing now is adequate, then there’s no benefit to more.

 

[lidl e]

Worrying g about getting the most power out of the amp isn’t important. If what you are doing now is adequate, then there’s no benefit to more.

Yes. But we are starting to play bigger shows now so I migh tneed more power. Will put what i have now to the test on a number of shows in October and make a more informed decision if i need something more end of the month.

 

[bassfran]

If you’re playing bigger shows and travelling I suggest having some kind of backup plan for an amp if even a D.I. box. Murphy’s Law, and all.

 

[SunByrne]

If you’re playing bigger shows and travelling I suggest having some kind of backup plan for an amp if even a D.I. box. Murphy’s Law, and all.

Murphy was an optimist.

 

[shirojiro]

In general I found that good 4x10 like your Goliath is sufficient for shows as large as a decent sized theater.

For bigger gigs like a festival stage or arena, there really needs to be a pretty big PA to project enough sound.

If you want more volume, a second 4x10 , either another Goliath or something with similar sensitivity will result in decent increase in volume because of several reasons including more speaker surface area, more wattage, coupling effects , and higher perceived volume from getting a cab next to your head.

But then you have another big cab to lug around.

The amp and Aguilar 1x12 are a nice combination for a smaller gig too.

 

[Pep]

While I've been playing for years i do have a bit of a rookie question. I do always try to match impedance, currently my only available amp head is a TC electronic bh250. The documentation says run a 4ohm load onto it.

I have only ever used it with a single 8ohm cab.

Am i risking anything by doing that? I never considered it was an issue. I didnt even realise the TC was considered 4ohm. I just happened to check the manual in prep of a few shows that are coming up.

I played some shows recently with a bigger band using the bh250 into a SWR Goliath III and it sounded great. I even let the headliner (the aquabats) use my setup and it sounded great.

We are about to do a mini tour and i was planning on using this setup but i wont have a backup if something goes wrong.

Am i right to be worried? I could conceivably bring an extra Aguilar 1x12 which is 8 ohms to give me 4ohm total but storage space is at a premium.

I dont really want to invest in another head. I do have an old SWR Mo Bass but i need to bring an external transformer to use that as it is from the US and I am im the EU.

I have used the tc into a single 8ohm speaker many times. The tc and the aggie cab seem to work well.

Cheers, all.

This may have already been stated. Your amp is rated at 4 ohms minimum so 4 is fine, but don’t go under that. 8 ohms isn’t a problem either.

 

[Wasnex]

While I've been playing for years i do have a bit of a rookie question. I do always try to match impedance, currently my only available amp head is a TC electronic bh250. The documentation says run a 4ohm load onto it.

I have only ever used it with a single 8ohm cab.

Am i risking anything by doing that? I never considered it was an issue.

There is a difference between solid state output sections and tube output sections.

Solid state output sections are usually concerned with the minimum impedance. Your amp is 4 ohms minimum. So you should not show it a lower load such as 2.67 ohms or 2 ohm. Anything higher than 4 ohms is fine, but most likely the amp will make less power as the impedance increases.


Tube output sections are usually concerned with impedance matching. The impedance of the output tubes is relatively high while the impedance of the speakers is relatively low. A transformer is used to match the high impedance to the low impedance. Some transformers have only one output tap while others have 2 or 3. Normally you show a tube amp the expected load (I.E. connect the expected impedance).

Some tube amps can handle a small impedance. Some amps are safe if the impedance is higher than expect, but not if the impedance is two low. Some amps are the opposite and are safe when impedance is lower than expected, but not higher. Some amps are safe with both. Some amps are safe with neither. With a safe impedance mismatch, the power the amp can produce will be reduced and wear will be increased on the output tubes. With an unsafe impedance mismatch, the damage can range from a blown fuse to blow tubes and blown transformers.

Under no circumstance should you operate a tube amp without a load connected to the speaker out. This load can be a speaker or a dummy load. Some tube amps even have a built in dummy load that is connected automatically until a speaker cord is inserted into the speaker jack. Most tube amps do not have this feature.

 

[dbsfgyd1]

Yes. But we are starting to play bigger shows now so I migh tneed more power. Will put what i have now to the test on a number of shows in October and make a more informed decision if i need something more end of the month.

Just a few things. What your you are looking for is not just more power, but more decibels. Even if you had a 4 ohm version of your existing cab, you likely would not notice much of an increase in decibels. The amount of dBs per watt depends on how efficient your cab(s) are.

As for having a a back-up of course something is better than nothing if something fails. As for adding a 112 cab as a meaningful addition to your current stage rig is not going to get you there. I would doubt you would even notice it’s plugged in. But as a back up in case your cab blows up might me useful.

One other thing is, on tour are you going to have FOH support? Good monitors? Sometimes you can get by with a direct out into the board and or a feed from the monitors.

Best wishes on a successful tour. Have fun!

 

[S-Bigbottom]

Keep doing what you are doing.

 

[Wasnex]

Cheers, bud.

Would adding the extra 1x12 be a good idea so id get the full power? I believe it is rated for 400 watts so shoildnt be an issue handling it. The SWR can take 500+

Is a 4x10 and a 1x12 an odd combo?

IMHO as long as the combination of cabs is safe, try it and judge for yourself. But in general I wouldn't expect a 410 and 112 to be a great combination. Adding a cab may or may not sound good and/or increase headroom.

The first concern is make sure the resulting load is safe for the amp. If both cabs are 8 ohms , the load is total load is 4 ohms which is the minimum your amp is rated for (safe).

The second concern is to make sure both cabs can handle the power they will receive. Usually when you use two cabs they are connected in parallel. Two 8 ohm cabs win parallel will share the power equally. So both cabs will receive 125W if the amp is adjusted to make 250W. As long as both cabs can handle 125W the combination should be relatively safe with this particular amp.

Whether adding a cab will result in more volume depends on how close their sensitivity ratings are and how much the power increases when you add the second cab. Sensitivity is usually expressed at 1W/1m. You might see Sensitivity = 100dB 1W/1m. This means when 1 Watt is applied, 100dB is measured at a distance of 1 meter. Most good 410s are usually more efficient than a 112. If the difference in sensitivity is 8dB or more, then adding the 12 will actually result in lower combined sensitivity rating.

Example:

• Let's say you have two identical cabs with Sensitivity rating of 100dB 1W/1m. The combined sensitivity of both cabs, assuming perfect summing, will be 103dB.
• If one cab has a sensitivity of 100dB and the other has a sensitivity of 92dB, the combined sensitivity of both cabs is 99.9dB
• We also need to consider what happens to the total power when a cab is added.
  • Assuming the amp doubles power when the impedance is cut in half, you get +3dB. So adding a cab still should give you slightly more headroom.
  • If the amp's power does not increase, then adding the inefficient cab decreases headroom.

The other factor is how well the cabs work together. The best combination is usually matching cabs because they have the same tuning. If you use cabs with drastically different tunings, it can result in poor sound quality because the cabs fight with each at some frequencies rather than working together. In some instances, adding a cab may noticeably increase perceived volume, but your sound may be bad or sort of disappear in the mix.

 

[Shoreline Gold]

Murphy was an optimist.

Ah yes, O'Neal's Corollary.

 

[agedhorse]

Yes. But we are starting to play bigger shows now so I migh tneed more power. Will put what i have now to the test on a number of shows in October and make a more informed decision if i need something more end of the month.

A second 8 ohm 210 will get you a LOT more than just more power into a single 4 ohm 210.

 

[Michedelic]

Cheers, bud.

Would adding the extra 1x12 be a good idea so id get the full power? I believe it is rated for 400 watts so shoildnt be an issue handling it. The SWR can take 500+

Is a 4x10 and a 1x12 an odd combo?

Do you already have access to a particular 4x10, and if so, what is the ohm rating/wattage?

 

[brianrost]

Yeah. Agreed but it would give me the full 250 watts, no?

For some stupid reason, TC can’t be bothered to show the power at 8 ohms in any of their documentation of any of their amps. The BH250 might be as low as 125 watts at 8 ohms.

I ve had zero issues with the BH250 driving 8 ohm Bergantino HT112 cabs rated for 300 watts. In fact, I’ve never run the volume up past 12:00. I only use two for outdoor gigs with no FOH support, 95% of my gigs only need one cab and I have no problems being loud enough.